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Optimism Testnet

Table of contents

  1. Previous steps: Install the FireFly CLI
  2. Create an evmconnect.yml config file
  3. Creating a new stack
  4. Start the stack
  5. Get some Optimism
    1. Confirm the transaction on Blockcscout
  6. Use the public testnet

Starting with FireFly v1.1, it’s easy to connect to public Ethereum chains. This guide will walk you through the steps to create a local FireFly development environment and connect it to the Optimism Goerli testnet.

Previous steps: Install the FireFly CLI

If you haven’t set up the FireFly CLI already, please go back to the Getting Started guide and read the section on how to Install the FireFly CLI.

← ① Install the FireFly CLI

Create an evmconnect.yml config file

In order to connect to the Optimism testnet, you will need to set a few configuration options for the evmconnect blockchain connector. Create a text file called evmconnect.yml with the following contents:

    required: 4 # choose the number of confirmations you require
    fixedGasPrice: null
        mode: connector

For this tutorial, we will assume this file is saved at ~/Desktop/evmconnect.yml. If your path is different, you will need to adjust the path in the next command below.

Creating a new stack

To create a local FireFly development stack and connect it to the Optimism testnet, we will use command line flags to customize the following settings:

  • Create a new Ethereum based stack named optimism with 1 member
  • Disable multiparty mode. We are going to be using this FireFly node as a Web3 gateway, and we don’t need to communicate with a consortium here
  • Use an remote RPC node. This will create a signer locally, so that our signing key never leaves the development machine.
  • See the optimism docs and select an HTTPS RPC endpoint.
  • Set the chain ID to 420 (the correct ID for the Optimism testnet)
  • Merge the custom config created above with the generated evmconnect config file

To do this, run the following command:

ff init ethereum optimism 1 \
    --multiparty=false \
    -n remote-rpc \
    --remote-node-url <selected RPC endpoint> \
    --chain-id 420 \
    --connector-config ~/Desktop/evmconnect.yml

Start the stack

Now you should be able to start your stack by running:

ff start optimism

After some time it should print out the following:

Web UI for member '0':
Sandbox UI for member '0':

To see logs for your stack run:

ff logs optimism

Get some Optimism

At this point you should have a working FireFly stack, talking to a public chain. However, you won’t be able to run any transactions just yet, because you don’t have any way to pay for gas. A testnet faucet can give us some OP, the native token for Optimism.

First, you will need to know what signing address your FireFly node is using. To check that, you can run:

ff accounts list optimism
    "address": "0x235461d246ab95d367925b4e91bd2755a921fdd8",
    "privateKey": "..."

Copy the address listed in the output from this command. Go to You will need to login to your Github account and paste the address in the form.

Optimism Faucet

Confirm the transaction on Blockcscout

You should be able to go lookup your account on Blockscout for Optimism testnet and see that you now have a balance of 100 OP. Simply paste in your account address to search for it.

Blockscout Scan

Use the public testnet

Now that you have everything set up, you can follow one of the other FireFly guides such as Using Tokens or Custom Smart Contracts. For detailed instructions on deploying a custom smart contract to Optimism, please see the Optimism docs for instructions using various tools.